<Page
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Grid ShowGridLines="True"> 
    <Grid.RowDefinitions><RowDefinition /><RowDefinition /></Grid.RowDefinitions>
     <Grid.ColumnDefinitions><ColumnDefinition /><ColumnDefinition /></Grid.ColumnDefinitions>
    
     <Button
        Foreground="#FFFF4500" Background="Black" 
        Grid.Row="1" TextBlock.FontSize="{Binding ElementName=fontsize,Path=Value}" Margin="30,30,30,30">
          <TextBlock Text="sample" FontSize="20"/> 
        </Button> 
  
      <Slider x:Name="fontsize" Minimum="12" Maximum="80" Value="40"/> 
  </Grid>
  
  
  
</Page>